The present invention pertains to medication dispensing devices, and, in particular, to a portable medication dispensing device such as an injector pen.
Patients suffering from a number of different diseases frequently must inject themselves with medication. To allow a person to conveniently and accurately self-administer medicine, a variety of devices broadly known as injector pens or injection pens have been developed. Generally, these pens are equipped with a cartridge including a piston and containing a multi-dose quantity of liquid medication. A drive member, extending from within a base of the injector pen and operably connected with typically more rearward mechanisms of the pen that control drive member motion, is movable forward to advance the piston in the cartridge in such a manner to dispense the contained medication from an outlet at the opposite cartridge end, typically through a needle that penetrates a stopper at that opposite end. In disposable pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, the entire pen is discarded by a user, who then begins using a new replacement pen. In reusable pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, the pen is disassembled to allow replacement of the spent cartridge with a fresh cartridge, and then the pen is reassembled for it subsequent use.
For an injector pen to be used optimally, just prior to using the pen to inject oneself with medicine, a user should prime that pen. During priming, the pen is operated to shift the cartridge piston a sufficient distance to force any air from the cartridge and to shift the cadge piston a sufficient distance to force any air from the cartridge and needle and cause medicine to reach the exposed distal or forward tip of the needle, such that the subsequent injecting use of the pen in fact delivers the volume of medicine the pen is arranged to deliver. Some users, however, fail to so prime the pen, resulting in an injecting of less medicine than presumably intended by the user.
One possible explanation for the failure to prime is that the design of most injector pens does not assist the user in conceptually distinguishing a priming step from a dose injecting step. In particular, the priming step typically involves setting the pen to deliver a small dose, operating the pen without injecting the user but otherwise in the same manner as would be performed during user injection, and then repeating these steps if necessary, until priming has been accomplished. Then, during the dose injecting step, the dose is actually set in exactly the same way as in the priming step but typically in a larger quantity, and then the pen is used to inject the medicine into the user.
U.S. Pat. No. 5,961,495 discloses an injection pen in which the priming control mechanism is by outward appearances distinct from the mechanism used to actually set and then inject the selected dose into a user. Dose setting and injection is accomplished with a dose knob at the proximal end of the pen housing. The dose knob is rotatable to set one of a number of dose quantities which are possible to select. Injection of the set dose is accomplished by pulling out the dose knob, and then pushing the knob in after the pen has been manipulated such that its injection needle has penetrated the user's skin. The priming mechanism utilizes a manually operable priming control sleeve that is spaced from the dose knob. The priming control sleeve is connected to the internal drive mechanism of the pen such that the sleeve can be manually rotationally pivoted back and forth as necessary to prime the pen in anticipation of the injection operation. While perhaps functional, this design is not without its shortcomings. For one thing, the adjustability in the setting of the dose to be injected results in a relatively complicated pen design, which may undesirably increase the cost of manufacture and assembly of the pen. The back and forth ratcheting action of the priming control sleeve possibly required to achieve pen priming also may be confusing or not intuitive to some users, who might therefore fail to prime the pen completely. In addition, the dose setting capacity of the pen is a potential source of dosing errors as the user who intends to inject the same quantity of medicine as injected the last time the pen was used may fail to pay proper attention to the dose actually set, which set dose may be different than what was set previously as a result of an inadvertent switching since the prior use.
Thus, it would be desirable to provide an apparatus that overcomes these and other shortcomings of the prior art.